In recent years, wind turbine generators which generate electric power using wind are becoming popular from the perspective of preserving the global environment. Generally, a wind turbine generator is configured to convert kinetic energy of wind into rotational energy of a wind turbine blade (i.e. the entire rotor including the wind turbine blade) and then to convert the rotational energy into electric power in a generator.
Generally, wind turbine blades are manufactured using a mold to obtain a desired aerofoil profile. As one example of typical manufacturing methods of wind turbine blades, Patent Literature 1 describes a manufacturing method in which a dry fiber sheet disposed on a mold is impregnated with resin and then the resin is hardened to produce a wind turbine blade. In this type of manufacturing method, normally only one type of wind turbine blade which fits the shape of the mold can be manufacture and it requires one mold for each aerofoil profile.
Further, it is proposed in Patent Literature 2 and Patent Literature 3 to retrofit the wind turbine blade by connecting an extension unit to a tip of the existing wind turbine blade to adjust performance of the wind turbine blade according to environment conditions.